Bottom emission type organic electroluminescent panel

ABSTRACT

Provided is a bottom emission type organic EL panel capable of preventing or delaying loss of light emission from an end portion of the light emission area and reduction of the light emission area in an organic EL element. This organic electro luminescence panel includes an organic electro luminescence element having at least one organic layer between an anode and a cathode arranged on a substrate. This panel has a main light emission area emitting light with a high luminance and a non-light emission area or a low light emission area emitting light with a lower luminance than the main light emission area, arranged outside the end portion of the main light emission area. By limiting the main light emission area to a smaller size than the cathode forming area, the end portion of the cathode forming area is arranged outside the end portion of the main light emission area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 12/159,126filed Jun. 25, 2008, which is a U.S. National Phase Application under 35U.S.C. 371 of International Application PCT/JP2006/324531 filed on Dec.8, 2006, which in turn claimed priority of Japanese Application No.2005-369322, filed Dec. 22, 2005, the priority of all is hereby claimed,and all the applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a bottom emission type organicelectroluminescent panel which is utilized for a flat light source and adisplay.

BACKGROUND ART

In recent years, an organic electroluminescent element (hereinafter,also referred to as an organic EL element) has been extensivelydeveloped. An organic EL element is a thin film element comprising atleast one layer of an organic layer (including an emission layer) beingsandwiched by electrode thin films, and applications thereof for variousdisplays, which are capable of obtaining emission colors from red toblue by forming the organic layer with (appropriate) selection amongfluorescent substances of various organic low molecular weigh compoundsand polymer compounds, have been studied.

A bottom emission type organic EL element is constituted of, forexample, transparent conductive film such as ITO film having beingpatterned as a bottom electrode on a transparent substrate, an organiclayer containing an emission layer in addition to cathode as areflective electrode which are accumulated on said anode, and emissionis taken out from the substrate side.

FIG. 1 is a drawing to show an example of a bottom emission type organicEL element of a simple matrix type. In a simple matrix type, ITO (indiumtin oxide) film is patterned into a stripe form to form transparentelectrode (anode) 2, organic layer 3 having been further provided, andthen cathode 4 (also referred to as a reflective electrode) comprisingsuch as aluminum is formed also in a stripe form so as to cross straightagainst the transparent electrode pattern (herein, this cathode layer isabbreviated in FIG. 1 (a) because it is formed covering the wholesurface).

In these elements, an overlapping portion of an anode and a cathodeforms an emission area, however, it has been proved that there caused aphenomenon to lose emission in the edge portion of a cathode in anemission area when light-on or current-on is continued for a long periodresulting in reduction of the light emission area (the region is 15 inFIGS. 1( a) and (b)). This is considered to be related to a cathode (areflective electrode) being present on the outside (the atmosphericside).

This invention provides a bottom emission type organic EL panel in whicharrangement of electrodes constituting said panel is designed to preventor restrain reduction of the aforesaid emission area Herein, it isdisclosed that improvement is intended by conducting sealing of anorganic EL by a cathode having an increased film thickness (for example,refer to patent document 1). However, in this document, it is sealing ofan active matrix organic EL panel, which is a relationship betweenorganic film and cathode film, and is different from relationshipbetween an emission area and a cathode area according to this invention.An only specific means disclosed to avoid contact of a cathode and awiring, which is caused by forming a cathode having a larger size thanorganic film, is a means by a sealing material. Further, since a cathodelayer thickness is increased, it is expected to cause a problem of suchas stress in an emitting substance having a relatively large area inthis invention.

Further, it is known an example of a segment emission organic EL elementof a bottom emission type in which thin film comprising a metal, whichis provided with a work function of not more than 4.8 eV such asaluminum, is arranged around an ITO electrode in a similar manner tothis invention (for example, refer to patent document 2), however, thepurpose is different from this invention.

Further, disclosed is a constitution to make an emission area to besmaller than cathode area by use of such as an insulation film or asupplemental electrode (for example, refer to patent documents 3 and 4).However, this invention proposes a method not only to make an emissionarea smaller than a cathode area but also to make a primary emissionarea smaller than a cathode area to form a constitution, in which a lowemission area and a cathode area are brought in contact to reduce aneffect of loss. Simultaneously, a means to make a main emission areasmaller than cathode area is also different.

Patent Document 1: JP-A 2003-178885 (hereinafter, JP-A refers toJapanese Patent Publication Open to Public Inspection)

Patent Document 2: JP-A 2000-357589

Patent Document 3: JP-A 2001-267066

Patent Document 4: JP-A 2000-21564

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of this invention is to provide an organic electroluminescentpanel equipped with bottom emission type organic electroluminescentelement (organic EL element), wherein reduction of an emission area dueto loss of emission from the edge portion of the emission area of saidelement is prevented or delayed.

Means to Solve the Problems

The above-described object of this invention has been achieved byfollowing constitutions 1-7.

1. A bottom emission type organic electroluminescent panel equipped withan electroluminescent element having an anode and a cathode on asubstrate and at least one organic layer between said anode and saidcathode, wherein a main emission area emitting light with a highluminance and a non-emission area or an emission area emitting lightwith a relatively lower luminance, which are arranged outside the edgeportion of said main emission area, are provided, and the edge portionof the aforesaid cathode area is arranged outside the edge portion ofthe aforesaid main light emission area by limiting the main emissionarea to a smaller size than the cathode forming area.

2. The bottom emission type organic electroluminescent panel describedin item 1, wherein an anode take-out part is arranged on the backsurface of a substrate equipped with the aforesaid anode, and said anodetake-out part is electrically connected with the aforesaid anode througha through hole arranged on said substrate.

3. The bottom emission type organic electroluminescent panel describedin item 1, wherein at least a part of the aforesaid anode is prolongedto the outer direction as an anode take-out part, an area provided withan organic layer having a layer thickness larger than the area, on whichother organic layer is formed, being present so as to overlap on saidanode take-out part, and a part of a cathode layer is formed so as tooverlap on at least a part of the aforesaid area on which a thickorganic layer is formed.

4. The bottom emission type organic electroluminescent panel describedin item 1, wherein at least one electron injection layer is arranged asa constituent layer of the aforesaid organic layer and the forming areaof said electron injection layer is limited to be narrower than thecathode forming area.

5. The bottom emission type organic electroluminescent panel describedin item 1, wherein the aforesaid anode is provided with an area havingbeen subjected to a surface treatment and an edge portion of a cathodeforming area is arranged outside of said area.

6. The bottom emission type organic electroluminescent panel describedin item 5, wherein the aforesaid surface treatment has been conductedvia a treatment process including at least a plasma treatment.

7. The bottom emission type organic electroluminescent panel describedin any one of items 1-6 is characterized by white emission.

Effects of the Invention

This invention has enabled to provide an organic electroluminescentpanel equipped with bottom emission type organic electroluminescentelement (organic EL element), wherein reduction of an emission area dueto loss of emission from the edge portion of the emission area of saidelement is prevented or delayed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing to show an example of a bottom emissiontype organic EL element of a simple matrix type.

FIG. 2 is a schematic drawing to show an example of an electrodestructure of an organic EL panel of this invention.

FIG. 3 is a schematic drawing to show an example of an electrodestructure of an organic EL panel of this invention.

FIG. 4 is a schematic drawing to show an example of an electrodestructure of an organic EL panel of this invention.

FIG. 5 is a schematic drawing to show an example of an electrodestructure of an organic EL panel of this invention.

FIG. 6 is a schematic drawing to show an example of an electrodestructure of an organic EL panel of this invention.

FIG. 7 is a schematic drawing to show an example of an electrodestructure of an organic EL panel of this invention.

FIG. 8 is a schematic drawing to show an example of an electrodestructure of an organic EL panel conventionally known.

DESCRIPTION OF THE SYMBOLS

-   1: substrate (support)-   2: anode (transparent electrode)-   2 a: insulating layer-   2 b: region having been subjected to surface treatment on anode 2-   3: organic layer (organic compound layer)-   3 a: organic layer having layer thickness different from organic    layer 3-   3 b: electron injection layer-   4: cathode (reflective electrode)-   5: through hole-   6: cathode take-out part-   7: anode take-out part-   8: main emission area-   9: non-emission area-   10: low-emission area

PREFERRED EMBODIMENTS TO CARRY OUT THE INVENTION

This invention constitutes a bottom emission type organicelectroluminescent panel characterized by arranging the edge portion ofthe forming surface of the aforesaid cathode outside of the edge portionof the light emitting area.

In an organic EL element of a simple matrix drive type shown in FIG. 1,each of the overlapped portions of an anode and a cathode crossingstraight emits light. In the case of a bottom emission type organic ELelement in which a transparent electrode (an anode such as ITO)/anorganic layer/a reflective electrode (a cathode such as aluminum) aresuccessively formed, reduction of an emission area from the portiondefined by the edge of a reflective electrode is a primary portion ofthe loss. That is, there caused a phenomenon to make the emission areasmaller than the reflective electrode width when light-on is continued.On the other hand, there caused no reduction of an emission area alongthe transparent electrode width direction. This is considered becauseinvasion of moisture or a gas such as oxygen from the outside isprevented due to said portion being covered by a reflective electrode.That is, electric current is flowing in an organic layer including anemission layer sandwiched between electrodes; however, it is consideredthat an emission function is lowered or destroyed due to change ormodification of an organic compound in the organic layer when such asmoisture or oxygen invades from the outside in this state.

Therefore, this invention can diminish the portion through whichmoisture invades by determining an area to emit light (an emission area)as much as possible by the pattern of a transparent electrode (forexample, ITO) or other means and forming a reflective electrode (acathode made of such as aluminum) as a pattern of a larger size thansaid area.

That is, in a bottom emission type organic EL panel in which atransparent electrode/an organic layer/a reflective electrode aresuccessively formed on a substrate, the portion through which moisturemay invade is diminished by determining an emission area as much aspossible by ITO as a transparent electrode and forming a reflectiveelectrode in a larger size than said emission area.

Further, it is possible to delay loss of emission area (reduction of anarea) by making a reflective electrode larger than the main emissionwithout making said electrode larger than the emission area (the totalof a main emission area and a low emission area) when a low emissionarea which emits light with a relatively low luminance is arrangedaround a main emission area which emits light with a relatively highluminance.

In the above, reduction of an emission area was explained in referenceto an organic EL panel of a simple matrix drive type shown in FIG. 1,however, the above-described way of thinking of this invention can beapplied to such as each pixel of not only a simple matrix drive type butalso a segment emission type panel such as an organic EL panel utilizedas a white light source and an organic EL panel by an active matrix typedrive.

In aforesaid patent document 2, in a bottom emission type organic ELelement, an organic EL element of a segment display type in which metalthin film having a work function of not more than 4.8 eV (such asaluminum thin film) is arranged outside of the region other than the ITOtransparent electrode, is disclosed, however, it is related to anorganic EL element of a segment display type in which the metal film isemployed not as a reflective electrode but in stead of an insulationfilm around the emission area by utilizing a function to restrain holeinjection; the purpose is different from this invention.

In this invention, the part may be utilized as a take-out electrode andit is important that an anode (a transparent electrode) is utilized todetermine an emission area and an area of a cathode (a reflectiveelectrode) is made larger than the transparent electrode to seal anelement.

In the following, this invention will be detailed in reference to FIGS.2-7, taking an organic EL element of a segment emission type as anexample.

FIG. 2 is a schematic drawing to show an example of an electrodestructure of an organic EL panel. A main emission area, a non-emissionarea and a low emission area utilized here will be explained inreference to FIG. 2 and FIG. 3.

FIG. 2( a) shows an example of a bottom emission type organic EL panelin which anode 2 (a transparent electrode comprising such as ITO thinfilm), further, organic layer 3 including such as an emission layer, andcathode 4 (as a material to form a cathode, metal thin film comprisingmetal having a work function of not more than 4.8 eV such as aluminum ispreferably utilized) are successively formed on a substrate (such asglass).

Herein, main emission area 8 is a region where only anode 2 (atransparent electrode), organic layer 3 (including an emission layer)and cathode 4 (a reflective electrode) are overlapped. That is, itcorresponds to the area of anode 2 in FIG. 2( a) and a main emissionarea 8 in FIG. 2( c). Further, FIG. 2( b) is a cross-sectional view ofFIG. 2( a). FIG. 2( c) is a drawing to show a state of organic EL panelemitting light. FIG. 2( d) is a drawing to show emission luminance alongcross section A-A of FIG. 2( c).

In FIG. 2( d), it is clear that an organic EL panel is constituted of anarea which emits light with a high luminance (luminance=Lh) and an areawhich does not emits light (luminance=0). Herein, emission area is onlyan area which emits light with a high luminance and said area whichemits light with a high luminance is a main emission area. An area whichdoes not emit light is a non-emission area.

This invention is characterized in that the edge portion of theaforesaid forming surface of a cathode is arranged outside of the edgeportion of an emission area; however, it is preferable that the formingarea of cathode 4 is larger than the emission area and a distance froman arbitrarily selectable edge portion of the forming area of cathode 4to the nearest edge portion of said emission area is not less than 200μm. This design is effective to prevent invasion of such as moistureinto a main emission area from the outer atmosphere, and is essentiallypossible to prevent or delay reduction of an emission area due to lossof light emission from the edge of a main emission area. FIG. 3 showsanother example of an organic EL panel of this invention.

FIG. 3( a) is from a drawing of an example of a bottom emission type ELpanel in which anode 2 (a transparent electrode comprising such as ITOthin film), organic layer 3 including such as an emission layer andcathode 4 are successively formed on substrate (such as glass) observedfrom the viewing surface.

Further, FIG. 3( b) is a drawing to show a cross-section of FIG. 3( a).FIG. 3( c) is a drawing to show a state of an organic EL panel of FIG.3( a) emitting light. FIG. 3( d) is a drawing to show emission luminancealong A-A cross-section of FIG. 3( c).

In FIG. 3( d), it is clear that an organic EL panel is constituted of anarea which emits light with a high luminance (luminance=Lh), an areawhich emits light with a low luminance (luminance=Ll) and an area whichdoes not emits light (luminance=0). Herein, emission area is constitutedof an area which emits light with a high luminance and an area whichemits light with a low luminance. Said area which emits light with ahigh luminance is a main emission area and said area which emits lightwith a low luminance is a low emission area. An area which does not emitlight is a non-emission area. Herein, a low luminance indicates aluminance relatively lower than a high luminance.

Herein, an emission area is an area which is emitting light regardlessto luminance and includes the both of a main emission area and a lowemission area

FIG. 4 is a schematic drawing of an example of an electrode structure ofan organic EL panel of this invention, and is characterized in thatanode take-out portion 7 is arranged on the light take-out surface sidewhich is a back surface of substrate 1 provided with anode 2, and saidanode take-out portion 7 is electrically connected with aforesaid anode2 via through hole 5 arranged on said substrate 1. Further, a part ofcathode 4 arranged on the back surface of substrate 1, on which theaforesaid anode take-out portion 7 is arranged, (also referred to as thelight take-out surface side) is utilized as cathode take-out portion 6.This design enables to assure anode take-out portion even when a cathodearea is made larger than an emission area. In this case, there is no lowemission area and a main emission area is identical with an emissionarea. FIG. 5 is also a schematic drawing to show an example of anelectrode structure of an organic EL panel of this invention; FIG. 5( a)is a schematic cross-sectional view of an organic EL panel of thisinvention; FIG. 5( b) shows an electrode structure of an organic ELpanel of this invention as a view from light take-out surface side (alsoreferred to as the back surface side of cathode 4 (the cathode formingsurface)) of the organic EL panel. FIG. 5 shows an example of a bottomemission type organic electroluminescent panel having a form, in whichorganic layer 3 and organic layer 3 a having a different layer thicknessfrom each other are successively formed on anode 2, an uncovered portionof which is provided as anode take-out area 7. Organic layer 3 a isarranged so as to have a larger thickness than organic layer 3. In thecase that the difference of thickness between organic layers is large,area 3 having a large thickness does not emit light. In this case, it ispossible to assure an anode take-out portion while making a cathode arealarger than an emission area. In this case, there is no low emissionarea and a main emission area is identical with an emission area.

When the difference of thickness between organic layers is small, area 3a where organic layer has a large thickness emits light with a lowluminance. In this case, the edge portion of a cathode area is emittinglight; however, a rate of loss which proceeds from the edge portion ofan emission area becomes slow due to the low luminance. In this case, amain emission area does not contact with the edge portion of a cathodearea and a low emission area contacts with the edge portion of a cathodearea.

FIG. 6 is also a schematic drawing to show an example of an electrodestructure of an organic EL panel of this invention, and show a bottomemission type organic electroluminescent panel having a form in which atleast one electron injection layer 3 b is arranged as a constituentlayer of organic layer 3, and a forming area of said electron injectionlayer 3 b is set to narrower than the forming area of cathode 4.

An area where an electron injection layer is not provided does not emitlight or emits with a low luminance due to difference of an electroninjection characteristic between an area where an electron injectionlayer is not provided and an area where an electron injection layer isprovided. When the difference of an electron injection characteristic islarge, an area where an electron injection layer is not provided doesnot emit light and forms a non-emission area. It is possible to assureanode take-out portion 7 while making a cathode forming area larger thanan emission area because an electron injection layer is set to benarrower than a cathode forming area.

FIG. 7 is also a schematic drawing to show an example of an electrodestructure of an organic EL panel of this invention, and shows a bottomemission type organic electroluminescent panel having a form in whichanode 2 is provided with area 2 b having been subjected to a surfacetreatment and the edge portion of a forming surface of cathode 4 isformed outside said area 2 b having been subjected to a surfacetreatment.

An area without a surface treatment does not emit light or emits with alow luminance. When the difference of a hole injection ability betweenan area with a surface treatment and an area without a surface treatmentis large, an area without a surface treatment does not emit light andforms a non-emission area. It is possible to assure anode take-outportion 7 while making a cathode forming area larger than an emissionarea because an area with a surface treatment is set to be narrower thana cathode forming area. When the difference of a hole injection abilitybetween an area with surface treatment and an area without surfacetreatment is small, an area without a surface treatment forms lowemission area 10 which emits light with a low luminance (FIG. 7( b)).

It is possible to assure anode take-out portion 7 while making a cathodeforming area 4 larger than a main emission area 8 because area 2 b witha surface treatment is set to be narrower than a cathode area. Herein, asurface treatment indicates a treatment to accompany washing andmodification action of the anode surface and to improve a hole injectionability from an anode. Listed are a plasma treatment by such as oxygenand argon, an UV ozone treatment and an excimer irradiation treatment,however, it is not limited thereto provided being accompanied with theaforesaid effect.

In the above, this invention has been explained in reference to anorganic EL panel of a segment display type having a rectangular emissionarea form, however, is not dependent on a form of an emission area.

As described above, since a main emission area is almost determined byan area where a transparent electrode is formed or by other means andnot determined by a cathode forming area, reduction of an emission areais not caused in almost of the circumference of an emission area. In thecase that a low emission area being determined by a cathode area, lossof an emission area (reduction of the area) from the edge of a lowemission area occurs, however, the loss speed is small compared to lossof an emission area from the edge of a main emission area which iscaused in the case of a main emission area being determined by a cathodeforming area.

In this invention, a cathode (a reflective electrode) functions as asealing layer to prevent invasion of moisture or oxygen into an organiclayer and prevents invasion thereof from the outer atmosphere. Even inthe case of sealing these elements with other sealing material (such asa sealing can and anti-moisture film), since it is essentially difficultto conduct complete sealing, an effect of this invention does not changealthough life time is totally prolonged.

In FIGS. 2-7, organic EL panel of this invention was explained inreference to an organic EL panel of a segment display type as anexample, however, is preferably applied in a panel of a segment emissiontype and is useful for an organic EL panel utilized as a white lightsource.

However, in addition to this, it can be preferably utilized in eachpixel of an organic EL panel of a simple matrix drive type and anorganic EL element of an active matrix drive type.

In the following, an organic EL element according to an organicelectroluminescent panel (hereinafter, also referred to as an organic ELpanel) of this invention will be explained.

<Organic EL Element>

Next, constituent layers of an organic EL panel according to thisinvention will be detailed. A bottom emission type organic EL panel ofthis invention, in which light is taken out from the substrate side, isconstituted by arranging a transparent electrode on a substrate as ananode and sandwiching organic layers, which are successively formed asfollows, between said anode and a cathode as a reflective electrode.

-   1. anode (transparent electrode)/emission layer/electron transport    layer/cathode (reflective electrode),-   2. anode (transparent electrode)/positive hole transport    layer/emission layer /electron transport layer/cathode (reflective    electrode),-   3. anode (transparent electrode)/positive hole transport    layer/emission layer/positive hole inhibition layer/electron    transport layer/cathode (reflective electrode),-   4. anode (transparent electrode)/positive hole transport    layer/emission layer/positive hole inhibition layer/electron    transport layer/cathode buffer layer/cathode (reflective electrode),-   5 anode/anode buffer layer/electron inhibition layer/emission    layer/positive hole inhibition layer/electron transport    layer/cathode.

<Anode>

As an anode according to an organic EL element of this invention, thosecomprising metal, alloy, a conductive compound, which is provided with alarge work function (not less than 4 eV), and a mixture thereof as anelectrode substance are preferably utilized. Specific examples of suchan electrode substance include a conductive transparent material such asmetal like Au, CuI, indium tin oxide (ITO), SnO₂ and ZnO. Further, amaterial such as IDIXO (In₂O₃—ZnO) which can prepare an amorphous andtransparent electrode, may be also utilized. As for an anode, theseelectrode substances may be made into a thin layer by a method such asevaporation or spattering and a pattern of a desired form may be formedby means of photolithography, or in the case of requirement of patternprecision is not so severe (not less than 100 μm), a pattern may beformed through a mask of a desired form at the time of evaporation orspattering of the above-described substance. When emission is taken outof this anode, the transmittance is preferably set to not less than 10%and the sheet resistance as an anode is preferably not more than a fewhundreds Ω/□. In case of bottom emission type organic EL element,emitted light is taken from anode. Therefore, transmitance is preferably10% or more, and indium tin oxide (ITO) is most preferred. Further,although the layer thickness depends on a material, it is generallyselected in a range of 10-1,000 nm and preferably of 10-200 nm.

<Cathode>

On the other hand, as a cathode according to this invention, metal,alloy, a conductive compound and a mixture thereof, which have a smallwork function (not more than 4 eV), are utilized as an electrodesubstance. Specific examples of such an electrode substance includessuch as sodium, sodium-potassium alloy, magnesium, lithium, amagnesium/copper mixture, a magnesium/silver mixture, amagnesium/aluminum mixture, a magnesium/indium mixture, analuminum/aluminum oxide (Al₂O₃) mixture, indium, a lithium/aluminummixture and rare earth metal. Among them, with respect to an electroninjection property and durability against such as oxidation, preferableare a mixture of electron injecting metal with the second metal which isstable metal having a work function larger than electron injectingmetal, such as a magnesium/silver mixture, a magnesium/aluminum mixture,a magnesium/indium mixture, an aluminum/aluminum oxide (Al₂O₃) mixtureand a lithium/aluminum mixture, and aluminum. As for a cathode, theseelectrode substances may be made into a thin layer by a method such asevaporation or spattering. Further, the sheet resistance as a cathode ispreferably not more than a few hundreds Ω/□ and the layer thickness isgenerally selected in a range of 10-1,000 nm and preferably of 50-200nm. Herein, to transmit emission, either one of an anode or a cathode ofan organic EL element is preferably transparent or translucent toimprove the mission luminance.

A cathode is generally formed as a reflective electrode; theabove-described metal is prepared in a layer thickness of 1-20 nm as acathode followed by formation of a conductive transparent material,which is listed in the explanation of an anode, whereby a transparent ortranslucent cathode can be prepared; and an element provided withtransparency of both of an anode and a cathode can be prepared.

Further, a bottom emission type organic EL element having an oppositelayer structure can be prepared by forming an anode with a reflectiveelectrode comprising such as gold to prepare a translucent cathode.

Next, organic layers (an injection layer, an inhibition layer andelectron transport layer) in an organic EL element of this inventionwill be explained.

<Injection Layer: Electron Injection Layer, Positive Hole InjectionLayer>

An injection layer is appropriately provided and includes an electroninjection layer and a positive hole injection layer, which may bearranged between an anode and an emission layer or a positive transferlayer, and between a cathode and an emission layer or an electrontransfer layer, as described above.

An injection layer is a layer which is arranged between an electrode andan organic layer to decrease an operating voltage and to improve anemission luminance, which is detailed in volume 2, chapter 2 (pp.123-166) of “Organic EL Elements and Industrialization Front thereof(Nov. 30, 1998, published by N. T. S Corp.)”, and includes a positivehole injection layer (an anode buffer layer) and an electron injectionlayer (a cathode buffer layer).

An anode buffer layer (a positive hole injection layer) is also detailedin such as JP-A 9-45479, 9-260062 and 8-288069, and specific examplesinclude such as a phthalocyanine buffer layer comprising such as copperphthalocyanine, an oxide buffer layer comprising such as vanadium oxide,an amorphous carbon buffer layer, and a polymer buffer layer employingconductive polymer such as polythiophene.

A cathode buffer layer (an electron injection layer) is also detailed insuch as JP-A 6-325871, 9-17574 and 10-74586, and specific examplesinclude a metal buffer layer comprising such as strontium and aluminum,an alkali metal compound buffer layer comprising such as lithiumfluoride, an alkali earth metal compound buffer layer comprising such asmagnesium fluoride, and an oxide buffer layer comprising such asaluminum oxide. The above-described buffer layer (injection layer) ispreferably a very thin layer, and the layer thickness is preferably in arange of 0.1 nm-5 μm although it depends on a raw material.

<Inhibition Layer: Electron Inhibition Layer, Positive Hole InhibitionLayer>

An inhibition layer is, as described above, provided according to needbeside basic constitution layers of organic thin layers. As a positivehole inhibition layer, for example, a positive inhibition layerdescribed in such as JP-A Nos. 11-204258 and 11-204359 and p. 237 of“Organic EL Elements and Industrialization Front Thereof (Nov. 30,1998), published by N. T. S Corp.)” is applicable to a positive holeinhibition (hole block) layer according to this invention.

A positive hole inhibition layer, in a broad meaning, is provided with afunction of electron transport layer, being comprised of a positive holeinhibition material having a function of transporting an electron but avery small ability of transporting a positive hole, and can improve therecombination probability of an electron and a positive hole byinhibiting a positive hole while transporting an electron. Further, aconstitution of an electron transport layer described later can beappropriately utilized as a positive hole inhibition layer according tothis invention.

On the other hand, an electron inhibition layer is, in a broad meaning,provided with a function of a positive hole transport layer, beingcomprised of a material having a function of transporting a positivehole but a very small ability of transporting an electron, and canimprove the recombination probability of an electron and a positive holeby inhibiting an electron while transporting a positive hole. Further, aconstitution of a positive hole transport layer described later can beappropriately utilized as an electron inhibition layer.

<Emission Layer>

An emission layer according to this invention is a layer to emits lightby recombination of an electron and a hole which are injected from anelectrode, an electron transport layer or a hole transport layer, andthe portion to emit light may be either the inside of an emission layeror the interface between an emission layer and the adjacent layer.

An organic EL panel according to this invention preferably contains ahost compound and a dopant compound which will be described in thefollowing. It is possible to further increase emission efficiencythereby.

A fluorescent dopant is roughly classified into a fluorescent dopantwhich emits fluorescence and a phosphorescent dopant which emitsphosphorescence.

A typical example of the former (a fluorescent dopant) includes coumarintype dye, pyran type dye, cyanine type dye, croconium type dye,squarylium type dye, oxobenzanthracene type dye, fluorescein type dye,rhodamine type dye, pyrylium type dye, perylene type dye, stilbene typedye, polythiophene type dye or rare earth complex type fluorescentsubstances.

A typical example of the latter (a phosphorescent dopant) is preferablya complex type compound containing metal of the 8th-10th groups of theperiodic table, more preferably an iridium compound and an osmiumcompound and most preferable among them is an iridium compound.Specifically, listed are compounds described in the following patentpublication.

The phosphorescent dopant of the present invention is a compound whereinemission from an excited triplet state thereof is observed, specificallyincluding a compound emitting phosphorescence at room temperature (25°C.), which is defined as a compound exhibiting a phosphorescence quantumefficiency of at least 0.01 at 25° C. However, the phosphorescencequantum efficiency is preferably at least 0.1.

Such as WO 00/70655, JP-A Nos. 2002-280178, 2001-181616, 2002-280179,2001-181617, 2002-280180, 2001-247859, 2002-299060, 2001-313178,2002-302671, 2001-345183 and 2002-324679, WO 02/15645, JP-A Nos.2002-332291, 2002-50484, 2002-332292 and 2002-83684, JapaneseTranslation of PCT International Application Publication No.2002-540572, JP-A Nos. 2002-117978, 2002-338588, 2002-170684 and2002-352960, WO 01/93642 pamphlet, JP-A Nos. 2002-50483, 2002-100476,2002-173674, 2002-359082, 2002-175884, 2002-363552, 2002-184582 and2003-7469, Japanese Translation of PCT International ApplicationPublication No. 2002-525808, JP-A 2003-7471, Japanese Translation of PCTInternational Application Publication No. 2002-525833, JP-A Nos.2003-31366, 2002-226495, 2002-234894, 2002-235076, 2002-241751,2001-319779, 2001-319780, 2002-62824, 2002-100474, 2002-203679,2002-343572 and 2002-203678.

A part of examples are shown below.

A mixture of a plurality of emission dopants may be used.

<Host Compound (Emission Host Compound, or Also Referred to Simply asHost)>

The host compound of the present invention refers to a compoundexhibiting a phosphorescence quantum yield of less than 0.01 duringphosphorescence emission at room temperature (25° C.).

An emission host (an emission compound) used in the present invention isnot specifically limited in terms of the structure, typically includinga carbazole derivative, a triarylamine derivative, an aromatic boranederivative, a nitrogen-containing heterocyclic derivative, a thiophenederivative, a furan derivative, a compound having a basic skeleton suchas an oligoaryrene compound, a carboline derivative or a diazacarbazolederivative (a diazacarbazole derivative indicates a derivative having aring structure wherein at least one of the carbon atoms of a hydrocarbonring constituting a carboline derivative is substituted with a nitrogenatom).

Of these, it is preferable to use a carboline derivative or adiazacarbazole derivative.

Specific examples of a carboline derivative or a diazacarbazolederivative are shown below. However, the present invention is notlimited to them.

Further, an emission host of this invention may be either a lowmolecular weight compound or a polymer compound having a repeating unit,in addition to a low molecular weight compound provided with apolymerizing group such as a vinyl group and an epoxy group (anevaporation polymerizing emission host).

An emission host is preferably a compound having a positive holetransporting ability and an electron transporting ability, as well aspreventing elongation of an emission wavelength and having a high Tg (aglass transition temperature). As specific examples of an emission hostcompounds described in the following Documents are preferable: Forexample, JP-A Nos. 2001-257076, 2002-308855, 2001-313179, 2002-319491,2001-357977, 2002-334786, 2002-8860, 2002-334787, 2002-15871,2002-334788, 2002-43056, 2002-334789, 2002-75645, 2002-338579,2002-105445, 2002-343568, 2002-141173, 2002-352957, 2002-203683,2002-363227, 2002-231453, 2003-3165, 2002-234888, 2003-27048,2002-255934, 2002-260861, 2002-280183, 2002-299060, 2002-302516,2002-305083, 2002-305084 and 2002-308837.

Further, plural types of host compounds well known in the art may beutilized in combination. Further, by utilizing plural types of dopantcompounds, it is possible to mix different emitting lights to obtain anarbitrary emission color. White emission is possible by adjusting a typeof a phosphorescent compound and the doping amount, and is applicablefor a white illumination and a backlight by means of segment display.

Color emitted by an organic EL element of this invention is determinedby color, which is a measured result by a spectral radiation luminancemeter CS-1000 (manufactured by Konicaminolta Sensing Co., Ltd.) beingapplied to CIE chromaticity coordinate, which is described in FIG. 4.16of p. 108, “New Edition of Color Science Handbook” (edited by JapanColor Association, published University of Tokyo Press, 1985).

An emission layer can be prepared by film formation of theabove-described compound by means of a thin film forming method wellknown in the art such as a vacuum evaporation method, a spin-coatmethod, a cast method, a LB method and an inkjet method. A layerthickness as an emission layer is not specifically limited; however, isgenerally selected in a range of 5 nm-5 μm and preferably of 5-200 nm.This emission layer may have a single layer structure comprising onetype or not less than two types of these phosphorescent compounds andhost compounds or may have an accumulated structure comprising plurallayers of an identical composition or different compositions.

<Positive Hole Transport Layer>

A positive hole transport layer contains a positive hole transportingmaterial having a function of transporting a positive hole, and in abroad meaning, a positive hole injection layer and an electroninhibition layer are also included in a positive hole transport layer. Asingle layer of or plural layers of a positive hole transport layer maybe provided.

A positive hole transport material is those having any one of a propertyto inject or transport a positive hole or a barrier property to anelectron, and may be either an organic substance or an inorganicsubstance. For example, listed are a triazole derivative, an oxadiazolederivative, an imidazole derivative, a polyallylalkane derivative, apyrazolone derivative, a phenylenediamine derivative, a allylaminederivative, an amino substituted chalcone derivative, an oxazolederivatives, a styrylanthracene derivative, a fluorenone derivative, ahydrazone derivative, a stilbene derivative, a silazane derivative, ananiline type copolymer, or conductive polymer oligomer and specificallypreferably such as thiophene oligomer.

As a positive hole transport material, those described above can beutilized, however, it is preferable to utilized a porphyrin compound, anaromatic tertiary amine compound and a styrylamine compound, andspecifically preferably an aromatic tertiary amine compound.

Typical examples of an aromatic tertiary amine compound and astyrylamine compound include N,N,N′,N′-tetraphenyl-4,4′-diaminophenyl;N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine(TDP); 2,2-bis(4-di-p-tolylaminophenyl)propane;1,1-bis(4-di-p-tolylaminophenyl)cyclohexane; N,N,N′,N′-tetra-p-tolyl4,4′-diaminobiphenyl;1,1-bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane;bis(4-dimethylamino-2-metyl)phenylmethane;bis(4-di-p-tolylaminophenyl)phenylmethane;N,N′-diphenyl-N,N′-di(4-methoxyphenyl)-4,4′-diaminobiphenyl;N,N,N′,N′-tetraphenyl-4,4′-diaminophenylether;4,4′-bis(diphenylamino)quarterphenyl; N,N,N-tri(p-tolyl)amine;4-(di-p-tolylamino)-4′-[4-(di-p-triamino)styryl]stilbene;4-N,N-diphenylamino-(2-diphenylvinyl)benzene;3-methoxy-4′-N,N-diphenylaminostilbene; and N-phenylcarbazole, inaddition to those having two condensed aromatic rings in a moleculedescribed in U.S. Pat. No. 5,061,569, such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NDP), and4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (MDTDATA),in which three of triphenylamine units are bonded in a star burst form,described in JP-A 4-308688.

Polymer materials, in which these materials are introduced in a polymerchain or constitute the main chain of polymer, can be also utilized.Further, an inorganic compound such as a p type-Si and a p type-SiC canbe utilized as a positive hole injection material and a positive holetransport material

This positive hole transport layer can be prepared by forming a thinlayer made of the above-described positive hole transport materialaccording to a method well known in the art such as a vacuum evaporationmethod, a spin coating method, a cast method, an inkjet method and a LBmethod. The layer thickness of a positive hole transport layer is notspecifically limited, however, is generally 5 nm-5 μm, more preferably 5nm-200 nm. This positive transport layer may have a single layerstructure comprised of one or not less than two types of the abovedescribed materials.

A positive hole transporting layer having a high p property in which isdoped with an impurity may be used. Examples of them are described inJP-A 4-297076, JP-A 2000-196140, JP-A 2001-102175 and J, Appl. Phys.,95, 5773 (2004).

<Electron Transport Layer>

An electron transfer layer is comprised of a material having a functionto transfer an electron, and an electron injection layer and a positivehole inhibition layer are included in an electron transfer layer in abroad meaning. A single layer or plural layers of an electron transferlayer may be provided.

Conventionally, as an electron transfer material utilized in a singlelayer of an electron transfer layer, and in an electron transfer layeradjacent to the cathode side against an emission layer in the case ofutilizing plural electron transfer layers, the following materials areknown.

An electron transfer material (including a positive hole inhibitionmaterial) is provided with a function to transmit an electron injectedfrom a cathode to an emission layer, and compounds conventionally wellknown in the art can be utilized by arbitrarily selection as a materialthereof.

Examples of a material utilized in this electron transfer layer(hereinafter, referred to as an electron transfer material) include suchas a nitro-substituted fluorene derivative, a diphenylquinonederivative, a thiopyradineoxide derivative, a heterocyclic tetracarbonicacid anhydride such as naphthaleneperylene, carbodiimide, afluorenylidenemethane derivative, anthraquinonedimethane and anthronederivatives, and an oxadiazole derivative. Further, a thiazolederivative in which an oxygen atom in the oxadiazole ring of theabove-described oxadiazole derivative is substituted by a sulfur atom,and a quinoxaline derivative having a quinoxaline ring which is known asan electron attracting group can be utilized as an electron transfermaterial. Polymer materials, in which these materials are introduced ina polymer chain or these materials form the main chain of polymer, canbe also utilized.

Further, a metal complex of a 8-quinolinol derivative such astris(8-quinolinol)aluminum (Alq),tris(5,7-dichloro-8-quinolinol)aluminum,tris(5,7-dibromo-8-quinolinol)aluminum,tris(2-methyl-8-quinolinol)aluminum, tris(5-methyl-8-quinolinol)aluminumand bis(8-quinolinol)zinc (Znq); and metal complexes in which a centralmetal of the aforesaid metal complexes is substituted by In, Mg, Cu, Ca,Sn, Ga or Pb, can be also utilized as an electron transfer material.Further, metal-free or metal phthalocyanine, or those the terminal ofwhich is substituted by an alkyl group and a sulfonic acid group, can bepreferably utilized as an electron transfer material. Further,distyrylpyrazine derivative, which has been exemplified as a material ofan emission layer, can be also utilized as an electron transfermaterial, and, similarly to the case of a positive hole injection layerand a positive hole transfer layer, an inorganic semiconductor such asan n-type-Si and an n-type-SiC can be also utilized as an electrontransfer material.

This electron transport layer can be prepared by forming a thin layermade of the above-described electron transport material according to amethod well known in the art such as a vacuum evaporation method, a spincoating method, a cast method, an inkjet method and a LB method. Thelayer thickness of an electron transport layer is not specificallylimited; however, is generally 5 nm-5 μm, and more preferably it is5-200 nm. This electron transport layer may have a single layerstructure comprised of one or not less than two types of the abovedescribed materials.

An electron transporting layer having a high n property in which isdoped with an impurity may be used. Examples of them are described inJP-A 4-297076, JP-A 2000-196140, JP-A 2001-102175 and J, Appl. Phys.,95, 5773 (2004).

<Substrate (also Referred to as Base Plate, Base Material or Support)>

Examples of a substrate according to an organic EL element of thisinvention includes glass, quartz and transparent resin film. Resin filmsinclude such as film comprised of polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polyether sulphone (PES), polyetherimide, polyether etherketone, polyphenylene sulfide, polyallylate,polyimide, polycarbonate (PC) and cellulose acetate propionate (CAP).

On the surface of resin film, an inorganic (e.g., silicon oxide, siliconnitride oxide) or organic cover layer or a hybrid cover layer comprisingthe both may be formed, and the film is preferably provided with a highbarrier ability having a vapor transmittance of not more than 0.01g/(m²·day-atm)

An organic EL panel can be made by forming sequentially theabove-described constitution layers on a substrate.

First, on an appropriate substrate such as glass plate, a thin layercomprising a desired electrode substance such as an anode electrodesubstance is formed by means of evaporation or spattering so as to makea layer thickness of not more than 1 μm and preferably of 10 nm -200 nm,whereby an anode is prepared.

Next, on this layer, thin layers containing organic substances (e.g.,hole injection layer, a positive hole transport layer, an emissionlayer, and an electron transport layer, an electron injection layer, anda positive hole inhibition layer) are formed. A thin layer formingmethod of these layers containing the organic substances includes suchas a vacuum evaporation method, a spin coat method, an ink-jet method,and a printing method. Further, a different layer forming methoddepending on each layer may be applied. In the case of employing anevaporation method in layer formation, the evaporation condition dependson such as the type of a utilized compound, however, is generallyappropriately selected in a range of 50-450° C. as a boat heatingtemperature, 10⁻⁶-10⁻² Pa as a vacuum degree, 0.01-50 nm/sec as adeposition rate, −50-300° C. as a substrate temperature and 0.1 nm-5 μm,more preferably 5 nm-200 nm as a layer thickness.

After formation of these layers, a thin layer comprising a cathodeelectrode substance is formed thereon by means of such as evaporation orspattering so as to make a layer thickness in a range of 50-200 nm toprovide a cathode, whereby a desired organic EL element can be prepared.This preparation of an organic EL element is preferably carried out withone time evacuation to prepare all through from a positive holeinjection layer to a cathode, however, different layer forming methodmay be also applied by taking out the element on the way. At that time,it is preferable to take consideration such as to perform the operationunder a dry inert gas environment. At this time, it is not preferable tomake the layer thickness of not more than 50 nm because reflectivity isdecreased to lower emission efficiency and to deteriorate sealingability. To make the layer thickness of a cathode large is preferablewith respect to sealing ability; however, it is not preferable to makethe layer thickness of not less than 200 nm because a problem of stresswill be generated.

Further, reversing the preparation order, it is also possible to preparean organic EL element in the order of a cathode, an electron injectionlayer, an electron transport layer, an emission layer, a hole transportlayer, a hole injection layer and an anode. In the case of applyingdirect voltage on a multicolor display apparatus thus prepared, emissioncan be observed when a voltage of approximately 2-40 V is appliedutilizing an anode as + and a cathode as −. Further, alternating voltagemay be also applied. Herein, the wave-form of alternating voltageapplied may be any form.

EXAMPLES

In the following, with respect to preparation of an organic EL elementaccording to this invention, a preferable embodiment will be explained.

A constitution of an organic EL element will be explained in referenceto FIG. 5.

Example 1

Preparation of a white emitting organic EL panel of a segment displaytype, which utilizes a glass plate as a substrate and has a constitutioncomprising an anode (a transparent electrode), organic layers (anexample provided with a hole injection layer/a hole transport layer/anemission layer/an electron transport layer/an electron injection layeras organic layers will be explained) and a cathode on said glass plate,as an example of an organic EL element will be explained in reference toFIGS. 5( a) and (b).

First, utilizing a substrate (NA45 manufactured by NH TechnoglassCorp.), comprising substrate 1 (a glass plate) having a size of 100mm×100 mm×1.1 mm (thickness) on which ITO (indium tin oxide) having beendeposited, the ITO film was patterned by means of photolithographyemploying resist. That is, after the portion other than a non-conductiveregion had been covered with resist, ITO film of the non-conductiveregion (the exposed portion) was removed by being immersed into a 25%hydrochloric acid aqueous solution. Thereafter, resist was removed byimmersion into a 1.5% sodium hydroxide aqueous solution, followed byfurther washing and drying.

A pattern of anode 2 (a transparent electrode) comprising ITO, whichwill be a display part having a size of 40 mm×40 mm, was formed at thecenter of a glass plate having a size of 100 mm×100 mm (refer to FIGS.(a) and (b)).

Next, the circumference of substrate 1 (a glass plate), on which apattern of anode 2 (a transparent electrode) had been formed, was covedwith a mask, and each organic layer constituting an organic EL elementwas formed by vacuum evaporation so as to cover anode 2 (refer to FIGS.5( a) and (b)).

Organic layer 3 and organic layer 3 a each were formed on the regioncovering the region of 60 mm×60 mm which covers anode 2 (a transparentelectrode) arranged at the center of substrate 1.

Herein, formation of each of organic layer 3 (such as a hole injectionlayer, a hole transport layer, an emission layer, an electron transportlayer and an electron injection layer) and organic layer 3 a (the layerthickness is different from organic layer 3, however, the layerstructure is the same) was conducted by employing a vacuum evaporationmethod in the following manner.

Substrate 1 (a glass plate), on which an ITO transparent electrodepattern had been formed as anode 2 (a transparent electrode), wascovered with a mask and fixed on a substrate holder of a vacuumevaporation system available on the market to successively form organiclayers in the following manner.

First, after a vacuum chamber had been evacuated down to 4×10⁻⁴ Pa, aresistance heating boat made of tantalum and containing m-MTDATXA wasapplied with current and evaporation at an deposition rate of 0.1 nm/secwas conducted to form a hole transport layer having a thickness of 40nm.

Thereafter, emission layers each were formed by accumulation in thefollowing constitution utilizing each composition of emission layer A orintermediate layers 1 and 2.

A resistance heating boat made of tantalum was charged with each of ahost compound and a dopant so as to make the following ratio and beingheated by applying current, whereby each emission layer was formed so asto have the described thickness by evaporation at a deposition rate of0.1 nm/sec.

Emission layer A: CDBP:Ir-15 (3%): layer thickness (25 nm)

Intermediate layer 1: L-98: layer thickness (3 nm)

Emission layer B: CDBP:Ir-16 (8%): layer thickness (10 nm)

Herein, CDBP:Ir-15 (3%): layer thickness (25 nm) in each emission layerindicates a deposited film having a thickness of 25 nm containing 3weight % of Ir-15, which is a dopant, against CDBP.

Next, L-98 was deposited in 10 nm thickness thereon as a hole inhibitionlayer.

Further, a heating boat filled with Alg₃ was heated with electriccurrent to provide an electron transport layer having a layer thicknessof 35 nm on the aforesaid hole inhibition layer at a deposition rate of0.1 nm/sec. However, a deposition thickness on the portion of 3 a inFIG. 7( a) was further increased to form an electron transport layerhaving a thickness of 100 nm. Herein, evaporation was conducted at asubstrate temperature of room temperature. Successively, 0.5 nm oflithium fluoride was deposited as a cathode buffer layer (an electroninjection layer).

Then, by use of the same vacuum evaporation system, 110 nm of aluminumwas deposited so as to cover organic layer 3 also utilizing a mask,whereby cathode 4 (a reflective electrode) was formed. Cathode 4 (areflective electrode) is comprised of a region of 80 mm×80 mm at thecenter of substrate 1.

In the above manner, an organic EL panel of this invention has beenprepared. Thereby, prepared can be a white light emitting organic ELpanel which has a constitution to cover a main emission area by cathode4 (a reflective electrode) in the circumference length of an emissionarea and has no edge portion of cathode 4 (a reflective electrode) wherean emission function will be damaged.

FIG. 5( b) is a drawing to show an emission area viewed from the side ofsubstrate 1; an area (also referred to as a region) of 40 mm×40 mm,where anode 2 (a transparent electrode) and cathode 4 (a reflectiveelectrode) overlap each other and thick portion 3 a of an organic layeris excluded, is main emission area 8.

Example 2

An organic EL panel was prepared in a similar manner to example 1,except that layer thickness of an electron transport layer formed on theportion of area 3 a was set to 50 nm.

Example 3

Another embodiment will now be explained with reference to FIG. 6. Anorganic EL panel was prepared in a similar manner to example 1. Anorganic layer was prepared in a similar constitution to organic layer 3of example 1, except that an electron injection layer was formed only onthe area (area of 50 mm×60 mm) (3(b) of FIG. 6) other than thecorresponding portion to an area of 10 mm×60 mm (3(a) of FIG. 5) whichis same as organic layer area 3 a of example 1. Preparation other thanformation of an electron injection layer was conducted in a similarmanner to example 1.

Example 4

Another embodiment will now be explained with reference to FIG. 7. Anorganic EL panel was prepared in a similar manner to example 1. An areaof 50 mm×60 mm (2(b) of FIG. 7), which is same as organic layer area 3,was subjected to a plasma treatment while masking the portioncorresponding to an area of 10 mm×60 mm (2(a) of FIG. 5) which is sameas organic layer 3 a of example 1. Thereafter, an organic layer wasformed including an area which had not been subjected to a plasmatreatment. An organic layer was formed in a same constitution as organiclayer area 3 of example 1. Preparation was conducted in a similar mannerto example 1 except the plasma treatment.

COMPARATIVE EXAMPLE

A comparative example will now be explained with reference to FIG. 8.Anode 2 having a stripe form of 60 mm×10 mm was formed by patterning anITO substrate of 100 mm×100 mm as shown in FIG. 8( a). Next, an organiclayer was formed in a constitution similar to organic layer 3 of example1 on an area of 80 mm×80 mm at the center of the substrate. Then, acathode was formed in a stripe form of 100 mm×60 mm as shown in FIG. 8(a).

After continuous drive for 1,000 hours of these panels at a constantcurrent to make an initial luminance of 1,000 cd/m², loss of theemission area (reduction of an emission area) was observed; the resultswill be shown in the following table.

TABLE 1 State of emission at edge portion of Loss of emission cathodearea area (reduction) Example 1 Non-emission Non Example 2 Low-emissionSmall Example 3 Low-emission Small Example 4 Low-emission SmallComparative Emission Large example

It has been proved from these results that there caused no loss of anemission area of a panel in a state that the edge portion of a cathodearea does not emit light. Further, it has been proved that there causedlittle loss of an emission area of a panel in a state that the edgeportion of a cathode area emits with a low luminance.

An organic EL panel of this invention can be utilized in such as a homeuse illumination, a car illumination, a backlight for a watch and aliquid crystal, an advertising sign board, a signal tower, a lightsource for a memory medium, a light source for electrophtographiccopier, a light source for an optical processor and a light source foran optical sensor; however, the application is not limited thereto.

An organic EL element of this invention can be applied for a displayapparatus such as a display device, a display and various emission lightsources. In a display, full color display is possible by employing threetypes, or blue, red and green emitting organic EL elements. A displaydevice and a display include such as a television, a personal computer,a mobile apparatus, an AV apparatus, a character broadcast display andinformation display in a car. In particular, organic EL of thisinvention may be utilized as a display apparatus to regenerate a stillimage or a dynamic image, and a drive method in the case of utilizing asa display device for dynamic image reproduction may be a simple matrix(passive matrix) method.

1. A bottom emission type organic electroluminescent panel equipped withan electroluminescent element comprising an anode and a cathode on asubstrate and at least one organic layer between the anode and thecathode, wherein the electroluminescent panel has: a main emission areaemitting light with a high luminance; and a non-emission area or a lowemission area emitting light with a relatively lower luminance than themain emission area, the non-emission area or a low emission area beinglocated outside an edge portion of the main emission area, provided thatan edge portion of a cathode forming area is arranged outside the edgeportion of the main light emission area by limiting the main emissionarea to a smaller size than the cathode forming area, wherein at leastone electron injection layer is provided as a constituent layer of theorganic layer and an area for forming the electron injection layer isnarrower than the cathode forming area.
 2. The bottom emission typeorganic electroluminescent panel of claim 1, wherein an emitted light isa white light.